RADIO AIDS TO MARINE NAVIGATION - Canadian Coast Guard

TABLE 3
U.S. WEST COAST LORAN-C CHAIN – GRI 9940
STATION
FALLON,
Nevada (1)
GEORGE,
Washington (1)
MIDDLETON,
California (1)
SEARCHLIGHT,
Nevada (1)
LATITUDE
LONGITUDE
(2)
39 33 06.74N
118 49 55.82W
47 03 48.10N
119 44 38.98W
38 46 57.11N
112 29 43.98W
35 19 18.31N
114 48 16.88W
FUNCTION
EMISSION
DELAY
THEORETICAL
BASELINE
TRAVEL TIME (3)
RADIATED
PEAK
POWER
MASTER — — 400 kW
W
SECONDARY
13796.90 m s 2796.90 m s 1400 kW
X SECONDARY 28094.50 m s 1094.50 m s 400 kW
Y SECONDARY 41967.30 m s 1967.30 m s 560 kW
(1) This station operated by United States of America.
(2) Based on WGS 84 Datum (Coordinate system for charting).
(3) Theoretical Baseline Travel Time is based on all-seawater transmission path between master and secondary.
TABLE 4
NORTH CENTRAL U.S. LORAN-C CHAIN – GRI 8290
STATION
HAVRE,
Montana (1)
BAUDETTE,
Minnesota (1)
GILLETTE,
Wyoming (1)
WILLIAMS LAKE,
BC
LATITUDE
LONGITUDE
(2)
48 44 38.59N
109 58 53.613W
48 36 49.95N
94 33 17.92W
44 00 11.1N
105 37 23.90W
51 57 58.88N
122 22 01.69W
FUNCTION
EMISSION
DELAY
THEORETICAL
BASELINE
TRAVEL TIME (3)
RADIATED
PEAK
POWER
MASTER — — 400 kW
W
SECONDARY
14786.56 m s 3786.56 m s 800 kW
X SECONDARY 29084.44 m s 2084.44 m s 400 kW
Y SECONDARY 45171.62 m s 3171.62 m s 400 kW
(1) This station operated by the United States of America.
(2) Based on WGS 84 (coordinate system for charting).
(3) Theoretical Baseline Travel Time is based on all-seawater transmission path between master and secondary.
Loran-C Coordinate Converters
Many of the Loran-C Coordinate Converters on the market do not compensate for the overland propagation errors caused
by radio waves travelling more slowly over land than they do over seawater. These converters assume that the radio
waves are travelling over an all seawater path from the transmitters to the ship. Because the amount of the time delay in
each pattern varies with location, as does the width for 1 microsecond in each pattern, and the angle of cut between
patterns, and which two patterns are being used for the position determination, there can be no over-all simple error
statement.
It is important to note that a Loran-C coordinate converter that does not incorporate the overland propagation corrections
(Additional Secondary Factor, or ASF) within its computations will produce a systematic geographic position error. This
error is often in the dangerous direction; namely, it will compute a position that is farther offshore. If you are transiting
along a coast, thinking that you are safely outside the dangerous shoals, you may find yourself closer to shore than you
think you are.
The Canadian Hydrographic Service (CHS) has determined the overland propagation (ASF) errors through actual
observations. The overland propagation corrections were incorporated into the lattices that were/are on CHS nautical
charts. These maps have been published maps showing the corrections to observed Time Differences (TDs) necessary to
6-4